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Sound




Prepared by: Victor R. Oribe
Nature of Sound
Sound waves are produced by longitudinal vibrations of
molecules in gases and other media.

This means that as a wave travels through a medium, the
molecules of the medium oscillate to and fro.
The energy of this vibration is carried by the involved
waves, which is brought to our brains for interpretation
as sound.
Sound waves that travel in air
come in contact with our
eardrums causing it to
vibrate.
Can sound waves travel in
solid?

Can sound waves travel in
liquid?

If yes give some situations or
examples.
Transmission of Sound Waves
The capacity of matter to transmit sound depends
upon its elasticity.
Elastic solid transmit sound well.


Inelastic solid like cloth, rubber, plastic and
sponge transmit sound poorly
Liquids, in general, are better conductors of
sound than gases.
Solid is considered as the best sound
transmitter.
Why is solid a better sound transmitter than
liquid and gas?
Waves are transmitted from
one place to another by the
vibration of particles of the
medium.
We know that particles in a
solid are closer to each other
than the particles in liquid
and in gas.
Therefore, sound waves are
transmitted faster and more
efficiently in solid than in
liquid and in gas.
The Velocity of Sound
                      Thunder is heard few second
                      after the flask of lightning.




An observer standing at a distance from a gun will
see the flash of light before hearing the sound of
the gunshot
An observer standing at a
                 distance from a fireworks
                 display will see the flash
                 of beautiful lights before
                 hearing the sound of
                 fireworks explosions.


These show that sound travels slower than
light.
The velocity of sound varies in different
media.
It depends on the elasticity and density of
the medium.
In general, the more elastic the medium, the
faster the sound can travel.
The sound can travel faster in a solid
medium than in liquid or gas because the
elasticity of solid is greater than that of
liquid and gases.
Sound
Assignment:

1. Why sound not transmitted in
   a vacuum?


2. A distant lightning can be seen
   several seconds before the
   accompanying thunder is
   heard. Why?
Properties of Sound Waves
1. Intensity and Loudness
    The quantitative description of the
    intensity of sound is determined by a
    sound level scale called the decibel
    scale.
   Sound intensity is the amount of sound
   energy flowing each second through a
   unit area perpendicular to the direction
   of propagation.
Sound
Sound
2. Reflection of Sound Waves
   A sound is reflected when it strikes
   another body.
   The reflected wave is called an echo.
               The reflecting surface has to be at
               least 17 meters away from the
               source in order for the echo to be
               distinct from the original sound.
               If the reflecting surface is less 17
               meters, the reflected sound wave
               just blends with and strengthens the
               original sound.
The reflection of sound wave is used in
determining ocean depths and the altitude of an
airplane.               A sound wave is sent out
                        from a ship toward the sea
                        floor.
                        A wave is reflected from the
                        bottom of the sea and the
                        reflected wave is detected
                        by a receiving device.
                        Using the recorded elapsed
                        time and velocity of sound
                        in water, the ocean depth
                        may be computed.
The airplane altitude, a sonic altimeter is used.




Sonic Altimeter is consists of a sound emitter and
a record that measures the time interval between
the emission of sound and reception of the echo.
The product of the time interval and speed of
sound in air at a given temperature divided by 2 is
the plane’s altitude.
Reflected   waves       can     also    cause
inconvenience to listeners.

Echoes from smooth curved walls or ceiling
can increase the intensity of sound in certain
parts of the room.

In some cases the problem is due to
reverberation (repeated echoes).
2. Refraction of Sound Waves
  Like all types of waves, sound also undergoes
  refraction when a change in medium or change
  in property of medium takes place.
On a clear sunny day, the earth’s
                          surface is hot.

                          This causes the temperature of
                          the air just above the surface of
                          the earth to rise.

The temperature of the lower layer of air is higher than the
layers above, hence sound should be traveling faster near
the surface of the earth.
This difference in the speed causes the refraction of sound
waves away from the surface.
On a clear night the layer of air
                     nearer the earth’s surface gets
                     cold faster; hence, the lower
                     layer of air is colder.




As a result, sound travels faster at the higher layer
than at the lower layer and is refracted toward the
earth’s surface.
The sound traveling with
                              air in the same direction is
                              bent toward the earth’s
                              surface.




The sound traveling against
the moving air is bent away
from the earth’s surface.
Questions:
1. What is an echo?
2. When an echo considered useful?
3. What happened to the sound waves when
   they pass from one medium to another of
   different density?
4. Why do sound waves bend
      a. away from the surface of the earth
         during daytime
      b. toward the earth’s surface during
         nighttime?
5. Differentiate intensity from loudness.
Kinds of Sound Waves
1. Audible Sound Waves
  Sound waves that can be detected by human
  ear.
  A sound waves with frequencies in the range
  of 20 to 20,000 Hz can be detected by human
  ear.
  This range varies from one individual to
  another.
2. Ultrasonic Waves
  Sound waves with a frequencies above
  20,000Hz are called ultrasonic waves.

  These waves can also reach human ear but are
  not detected.
  This ultrasonic sound can be detected by some
  animals
  Dogs can hear sounds as high as 50,000 Hz,
  while bats can hear as high as 100,000 Hz
Ultrasonic Waves in the field of Medicine




Ultrasonic waves are used to
probe human organs instead of
X-rays.
Unlike X-rays, ultrasonic
waves does not damage human
tissue.
3. Infrasonic Waves
  Sound waves with frequencies below 20 Hz.


  Common source of this waves are vibrating
  heavy machines, earthquake, thunder, and
  volcanic eruption.


  These waves are audible but can cause damage
  to the human body.
How Much Have You Learned?

1. Differentiate ultrasonic from
   infrasonic.
2. How is ultrasonic waves
   utilized in the field of medicine?
Detection of Sound



                         Human and animals have a
                         very sensitive detector of
                         sound – the Ear.




The cross-section of human ear is almost similar to that
of other vertebrates.
The ear, which is the peripheral auditory system, is
divided into three parts:
The outer ear called the
                         pinna, collects the sound
                         waves and concentrates them
                         into ear canal to a limited
                         extent.


                         This canal transmits the
                         sound waves to the eardrum.


It also protects the eardrum from shock and intrusion by
external objects.
Air vibration set the eardrum
membrane in motion which in
turn causes the three little
bones (hammer, anvil, and
stirrup) to move.

These three little bones
convert the small amplitude
vibrations of the eardrum into
larger-amplitude oscillations
and transfer them to the inner
ear through the oval window.
Behind this oval window is a
                     snail-shaped,     liquid-filled
                     organ called cochlea to where
                     auditory      nerves        are
                     connected.

                     The       larger     amplitude
                     oscillations create travelling
                     waves that are transformed
                     into impulses sent to the brain
                     through the auditory nerves.
The brain relates and interprets the sound heard to
those previously experienced.
Hearing Damage
1. Noise with an intensity level above 120dB is
considered as an undesirable pollutant in our
environment.

2. Exposure to loud sounds (80dB or above) for a
long period can cause temporary hearing loss.

3. Overexposure to amplified rock music and noise
produced by machineries in factories and other
industrial establishment has been mostly the cause
of hearing damage.
4. Our human ear has a built-in muscular control in
the middle ear.

This limit the potential damage to the ear caused by
sustained loud sound.

But our ear cannot react rapidly to protect itself
against sudden bursts of short but very loud sounds
like gunshots or bomb explosions.

If the sound produced is too loud, it can force an ear
mechanism to go beyond its elastic limit, in this
case, the hearing damage becomes permanent.
5. Permanent hearing loss may also be caused by
physical damage to ear due to diseases, drugs with
side effects, or the natural aging process.
6. Infection of the middle ear due to unhygienic
practices can result to hearing damage.

7. Hearing damage can also occur to a fetus if the
pregnant mother suffered from measles or rubella
within the first trimester of pregnancy.

Rubella can cause malformation of the parts of the
fetus’ inner ear.
8. Drugs such as streptomycin have been found to
cause permanent hearing loss to small children.

Ringing in the ears while the child is under
medication is a symptom of such hearing damage.

Because of this, the use of this drug has been
carefully controlled.

9. A person may also permanently lose his or her
sense of hearing due to normal aging of the auditory
system.

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Sound

  • 2. Nature of Sound Sound waves are produced by longitudinal vibrations of molecules in gases and other media. This means that as a wave travels through a medium, the molecules of the medium oscillate to and fro. The energy of this vibration is carried by the involved waves, which is brought to our brains for interpretation as sound. Sound waves that travel in air come in contact with our eardrums causing it to vibrate.
  • 3. Can sound waves travel in solid? Can sound waves travel in liquid? If yes give some situations or examples.
  • 4. Transmission of Sound Waves The capacity of matter to transmit sound depends upon its elasticity. Elastic solid transmit sound well. Inelastic solid like cloth, rubber, plastic and sponge transmit sound poorly
  • 5. Liquids, in general, are better conductors of sound than gases.
  • 6. Solid is considered as the best sound transmitter.
  • 7. Why is solid a better sound transmitter than liquid and gas?
  • 8. Waves are transmitted from one place to another by the vibration of particles of the medium. We know that particles in a solid are closer to each other than the particles in liquid and in gas. Therefore, sound waves are transmitted faster and more efficiently in solid than in liquid and in gas.
  • 9. The Velocity of Sound Thunder is heard few second after the flask of lightning. An observer standing at a distance from a gun will see the flash of light before hearing the sound of the gunshot
  • 10. An observer standing at a distance from a fireworks display will see the flash of beautiful lights before hearing the sound of fireworks explosions. These show that sound travels slower than light.
  • 11. The velocity of sound varies in different media. It depends on the elasticity and density of the medium. In general, the more elastic the medium, the faster the sound can travel. The sound can travel faster in a solid medium than in liquid or gas because the elasticity of solid is greater than that of liquid and gases.
  • 13. Assignment: 1. Why sound not transmitted in a vacuum? 2. A distant lightning can be seen several seconds before the accompanying thunder is heard. Why?
  • 14. Properties of Sound Waves 1. Intensity and Loudness The quantitative description of the intensity of sound is determined by a sound level scale called the decibel scale. Sound intensity is the amount of sound energy flowing each second through a unit area perpendicular to the direction of propagation.
  • 17. 2. Reflection of Sound Waves A sound is reflected when it strikes another body. The reflected wave is called an echo. The reflecting surface has to be at least 17 meters away from the source in order for the echo to be distinct from the original sound. If the reflecting surface is less 17 meters, the reflected sound wave just blends with and strengthens the original sound.
  • 18. The reflection of sound wave is used in determining ocean depths and the altitude of an airplane. A sound wave is sent out from a ship toward the sea floor. A wave is reflected from the bottom of the sea and the reflected wave is detected by a receiving device. Using the recorded elapsed time and velocity of sound in water, the ocean depth may be computed.
  • 19. The airplane altitude, a sonic altimeter is used. Sonic Altimeter is consists of a sound emitter and a record that measures the time interval between the emission of sound and reception of the echo. The product of the time interval and speed of sound in air at a given temperature divided by 2 is the plane’s altitude.
  • 20. Reflected waves can also cause inconvenience to listeners. Echoes from smooth curved walls or ceiling can increase the intensity of sound in certain parts of the room. In some cases the problem is due to reverberation (repeated echoes).
  • 21. 2. Refraction of Sound Waves Like all types of waves, sound also undergoes refraction when a change in medium or change in property of medium takes place.
  • 22. On a clear sunny day, the earth’s surface is hot. This causes the temperature of the air just above the surface of the earth to rise. The temperature of the lower layer of air is higher than the layers above, hence sound should be traveling faster near the surface of the earth. This difference in the speed causes the refraction of sound waves away from the surface.
  • 23. On a clear night the layer of air nearer the earth’s surface gets cold faster; hence, the lower layer of air is colder. As a result, sound travels faster at the higher layer than at the lower layer and is refracted toward the earth’s surface.
  • 24. The sound traveling with air in the same direction is bent toward the earth’s surface. The sound traveling against the moving air is bent away from the earth’s surface.
  • 25. Questions: 1. What is an echo? 2. When an echo considered useful? 3. What happened to the sound waves when they pass from one medium to another of different density? 4. Why do sound waves bend a. away from the surface of the earth during daytime b. toward the earth’s surface during nighttime? 5. Differentiate intensity from loudness.
  • 26. Kinds of Sound Waves 1. Audible Sound Waves Sound waves that can be detected by human ear. A sound waves with frequencies in the range of 20 to 20,000 Hz can be detected by human ear. This range varies from one individual to another.
  • 27. 2. Ultrasonic Waves Sound waves with a frequencies above 20,000Hz are called ultrasonic waves. These waves can also reach human ear but are not detected. This ultrasonic sound can be detected by some animals Dogs can hear sounds as high as 50,000 Hz, while bats can hear as high as 100,000 Hz
  • 28. Ultrasonic Waves in the field of Medicine Ultrasonic waves are used to probe human organs instead of X-rays. Unlike X-rays, ultrasonic waves does not damage human tissue.
  • 29. 3. Infrasonic Waves Sound waves with frequencies below 20 Hz. Common source of this waves are vibrating heavy machines, earthquake, thunder, and volcanic eruption. These waves are audible but can cause damage to the human body.
  • 30. How Much Have You Learned? 1. Differentiate ultrasonic from infrasonic. 2. How is ultrasonic waves utilized in the field of medicine?
  • 31. Detection of Sound Human and animals have a very sensitive detector of sound – the Ear. The cross-section of human ear is almost similar to that of other vertebrates.
  • 32. The ear, which is the peripheral auditory system, is divided into three parts:
  • 33. The outer ear called the pinna, collects the sound waves and concentrates them into ear canal to a limited extent. This canal transmits the sound waves to the eardrum. It also protects the eardrum from shock and intrusion by external objects.
  • 34. Air vibration set the eardrum membrane in motion which in turn causes the three little bones (hammer, anvil, and stirrup) to move. These three little bones convert the small amplitude vibrations of the eardrum into larger-amplitude oscillations and transfer them to the inner ear through the oval window.
  • 35. Behind this oval window is a snail-shaped, liquid-filled organ called cochlea to where auditory nerves are connected. The larger amplitude oscillations create travelling waves that are transformed into impulses sent to the brain through the auditory nerves. The brain relates and interprets the sound heard to those previously experienced.
  • 36. Hearing Damage 1. Noise with an intensity level above 120dB is considered as an undesirable pollutant in our environment. 2. Exposure to loud sounds (80dB or above) for a long period can cause temporary hearing loss. 3. Overexposure to amplified rock music and noise produced by machineries in factories and other industrial establishment has been mostly the cause of hearing damage.
  • 37. 4. Our human ear has a built-in muscular control in the middle ear. This limit the potential damage to the ear caused by sustained loud sound. But our ear cannot react rapidly to protect itself against sudden bursts of short but very loud sounds like gunshots or bomb explosions. If the sound produced is too loud, it can force an ear mechanism to go beyond its elastic limit, in this case, the hearing damage becomes permanent.
  • 38. 5. Permanent hearing loss may also be caused by physical damage to ear due to diseases, drugs with side effects, or the natural aging process. 6. Infection of the middle ear due to unhygienic practices can result to hearing damage. 7. Hearing damage can also occur to a fetus if the pregnant mother suffered from measles or rubella within the first trimester of pregnancy. Rubella can cause malformation of the parts of the fetus’ inner ear.
  • 39. 8. Drugs such as streptomycin have been found to cause permanent hearing loss to small children. Ringing in the ears while the child is under medication is a symptom of such hearing damage. Because of this, the use of this drug has been carefully controlled. 9. A person may also permanently lose his or her sense of hearing due to normal aging of the auditory system.